How and why we test

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Testing the water

The perception many of us have that our coasts and freshwaters are some of the cleanest in the world is well founded and many sites are suitable to swim in. However, there are some sites which are likely to be not suitable for swimming because of a risk of faecal contamination.

These web pages provide you with information on the general suitability for swimming of popular sites in Canterbury this summer. Before you head off to the beach, the lake or the river, check this summer’s swimming grade of your swimming spot. This grading allows you to make informed decisions about where, when and how to use the sea, lakes and rivers for swimming and other recreational activities.

All sites are graded at the start of summer each year. The grade does not change during the summer. The grading indicates the general human health risk when swimming at a particular site but does not represent the health risk at any particular time.

The grading system is based on 2 types of information:

Potential contamination risks close to swimming spots such as sewage outfalls, stormwater drains, stock in waterways, water-fowl and run-off from land (Sanitary Inspection Category).

Water quality data for the site gathered over the past few years: Water quality data collected at a site over the previous 3 to 5 summers are used to calculate the water quality grade (Microbiological Assessment Category).

Suitability for recreation grades are determined using the following table:

Apart from a grading system for assessing the suitability of sites for contact recreation (e.g. swimming), the national guidelines also detail a sampling protocol for ongoing monitoring of water quality during the summer.

Weekly summer monitoring

Environment Canterbury monitors water quality at popular swimming spots throughout the Canterbury region during summer. Water samples are collected weekly from around 100 recreational swimming sites from mid-November to February/March.

The results are updated on this website as they are received from the laboratory and are generally available 48 hours after the sample was collected. The data are accessible by clicking on the swimming spots in the map.

You are cautioned to consider carefully before using the weekly data to make decisions that may concern public health or the conduct of business that may involve monetary or operational consequences.

It is the grading that should primarily be used to determine whether a particular site is suitable for swimming. The weekly data shown in this summer’s graphs alone are a less reliable tool to determine the risk to human health when swimming at a certain site as faecal contamination levels can vary widely from day-to-day and yesterday’s results do not guarantee the water is clean enough today.

The weekly results are:

Used to asses short-term variation (i.e. week-to-week) in microbiological concentrations

Accumulated and used for the annual calculation of the site grade (ideally based on 5 years of data)

Used to assess any immediate health risk, for example when water quality becomes unsuitable for swimming.

Some sites that have been monitored in the past are no longer sampled as they were consistently graded as either very good or very poor. Those sites that were consistently very poor and are no longer sampled have permanent signs to warn of the potential health risks of swimming there. Sites that were consistently graded as “very good” and that are not at risk of contamination, do not require regular monitoring.

What are we looking for in samples?

The samples are analysed for faecal indicator bacteria. These bacteria are an indicator of faecal contamination from warm-blooded animals, which is in turn an indication of the likely presence of pathogens (disease-causing organisms such as bacteria and viruses). Faeces can get into waterways from many different sources.

It is impractical to measure the pathogens directly, so indicator bacteria are used to alert us to possible health risks presented by the pathogens. These indicator bacteria occur naturally in the gut of warm- blooded animals (humans, birds, dogs, sheep, cows etc.) and do not pose a significant risk to human health themselves. Illnesses related to toxic substances – such as heavy metals or PCBs – are not measurable with indicator bacteria and are not covered by this monitoring programme.

Different indicator bacteria are used for marine and freshwater sites:

Escherichia coli (E. coli) are the indicator bacteria used for freshwater monitoring.

Enterococci are the indicator bacteria used for marine waters.

In most communities, the sewage effluent produced will contain pathogens all year round, and the guidelines are designed for use under such conditions. However, when there is an outbreak of a potentially waterborne disease in the community, and where that community’s sewage is discharged directly into or close to recreational waters without adequate treatment, the guidelines are not suitable. Under these circumstances, the relationship between indicator bacteria and pathogen concentrations may be different and the guideline values are be appropriate.

What do we do when there are high results?

Depending on the concentration of indicator bacteria found in samples, the national guidelines recommend different actions to be taken. These are summarised in the table below.